The present invention relates to an interlocking device for a push-button switch used for the operation of cranes and hoists, for example. More specifically, it relates to an interlocking device of a push-button switch including a switch body having fixed contacts provided with two push buttons, having mobile contacts, facing each other and being downwardly movable in multiple stages by being pressed.
On a conventional push-button switch used for the operation of cranes and hoists, an interlocking member for the push button is swingably provided with approximately the mid-point of two push buttons, provided face to face with each other. The interlocking member acts as a fulcrum to prevent simultaneous pressing down of the two push buttons, so that the operator may not press down the two push buttons simultaneously by mistake, causing reckless run or other trouble of the equipment (U.S. Pat. No. 5,045,647).
Also, when the conventional interlocking device for a push-button switch is applied a push-button switch having a pair of push buttons facing each other and being downwardly movable in multiple stages, or in three stages for example, a problem was that, to enable pressing down in three stages of either push button while preventing simultaneous pressing down of the two push buttons, it was impossible to maintain a large degree of freedom of a relative operating range between the two push buttons and the interlocking member due to the structure of this interlocking device, thus making it difficult to maintain a sufficient stroke in each stage of the push buttons and thereby causing a drop of operability of the push buttons.